Assessment of heat stress and cloudiness probabilities in post-flowering of spring wheat and canola in the Southern Cone of South America

RIVELLI, GONZALO MARTÍN; FERNÁNDEZ LONG, MARÍA ELENA; ABELEDO, LEONOR GABRIELA; CALDERINI, DANIEL FERNANDO; MIRALLES, DANIEL JULIO; RONDANINI, DEBORAH PAOLA

THEORY & APPLICATION CLIMATOLOGY

SPRINGER WIEN

Año: 2021

0177-798X

Episodes of heat stress constrain crop production and will be aggravated in the near future according to short and mediumterm climate scenarios. Global increase in cloudiness has also been observed, decreasing the incident solar radiation. Thiswork was aimed to quantify the probability of occurrence of heat stress and cloudiness, alone or combined, during the typicalpost-flowering period of wheat and canola in the Southern Cone of South America. Extended climate series (last 3?5 decades with daily register) of 33 conventional weather stations from Argentina, Brazil, Chile and Uruguay (23 to 40°S) wereanalysed considering the period from September to December. Two different daily events of heat stress were determined: (i)maximum daily temperature above 30 °C (T>30 °C) and (ii) 5 °C above the historical average maximum temperature of thatday (T + 5 °C). A cloudiness event was defined in our work as incident solar radiation 50% lower than the historical averageradiation of that day (R50%). The T > 30 °C event increased its probability of occurrence throughout the post-floweringphase, from September to December. By contrast, the risk of T + 5 °C event decreased slightly, just like for R50%, and thehigher the latitude, the lower the probability of R50%. The T>30 °C plus R50% combined stresses reached greater cumulatedprobabilities during post-flowering, compared to T+ 5 °C plus R50%, being 42% vs 15% in northernmost locations, 26% vs.19% in central (between 31 and 35°S) and 28% vs. 1% in southernmost locations, respectively. A curvilinear relationshipemerged between the monthly probability of combined stresses and the number of days with stress per month. In summary,T > 30 °C was the most frequent thermal stress during post-flowering in wheat and canola. Both combined stresses had anoticeable risk of occurrence, but T > 30 °C plus R50% was the highest. Evidence of the recent past and current occurrenceof heat stress individually, and its combination with cloudiness events during post-flowering of temperate crops, serves as abaseline for future climate scenarios in main cropped areas in the Southern Cone of South America